Slim is in


By James Tarr
Photos by Mark Fingar

This article was originally printed in Guns & Ammo Magazine.

Daniel Defense’s new DD4 RIII shows a blend of features that military, law enforcement, and civilian end-users have been asking for. 

The differences between the M4A1 that Daniel Defense has been selling for years and the new DD4 lower are fully bilateral (ambidextrous) operating controls, a longer gas system, and the new M-LOK handguard. Let’s dive into the details.

Even with rifles destined for the commercial market, Daniel Defense builds the crucial components to military spec. The bolt-carrier group and the barrel are HP MPI tested. I was sent the 16-inch version of the M4A1 RIII for testing, and the chromoly vanadium steel, cold hammer forged barrel sports a government profile, 5.56 NATO chamber and a 1:7-inch twist, chrome-lined bore. It is tipped with Daniel Defense’s flash hider with five slots and a solid bottom.

Instead of the carbine-length gas system found on the M4A1, this RIII version has a mid-length gas system. There are good reasons to go mid-length gas over carbine-length in 14.5- to 16-inch barrels. The longer gas system slows down the bolt, which increases its life and slightly reduces felt recoil. But that’s not the only reason DD used this gas system.

There are four versions of the DD4 RIII:

  • DD4 RIII: 16-inch barrel, mid-length gas, RIS III 12.5-inch rail
  • M4A1 RIII: 14.5-inch barrel, mid-length gas, RIS III 12.5-inch rail, pinned muzzle device
  • DD4 RIII S: 11.5-inch barrel, carbine-length gas, RIS III 10.5-inch rail
  • MK18 RIII: 13.3-inch barrel, carbine-length gas, RIS III 9.5-inch rail

Daniel Defense is heavily involved in military contracts. For over two decades, those of us paying attention to the long guns wielded by our special operations troops have been aware of the USSOCOM (United States Special Operations Command) SOPMOD (Special Operations Peculiar MODification) kit for the M4 carbine. Think of it as an approved accessory upgrade kit for the M4.

However, that’s all it was — new and improved accessories to hang on the quad rail-equipped M4. None of the approved bits and pieces in the SOPMOD “Block I” or “Block II” kits offered any improvement to the functioning of the rifle; they were all external.

But now we have the new URG-I (Upper Receiver Group- Improved), which some people are calling the SOPMOD Block III. This is an entirely new upper receiver assembly meant to provide improved reliability, durability, ergonomics, and accuracy over the original M4 top end. Spec’d for the URG-I is a Daniel Defense government profile 14.5-inch barrel with a MK12 low profile (pinned) gas block and midlength gas system, the same barrel/gas block you see in this M4A1 RIII.

This softer recoiling upper was important to the military because the new gun must withstand the military’s current issue M855A1 ammo, which tends to eat barrels faster than previous issue ammo due to its copper, solid- core construction and a still-classified but high chamber pressure. Because the gas port is further from the chamber on a mid-length gun, the pressure at the gas port is lower, reducing erosion.

The military also decided to ditch old school quad rails for an M-LOK handguard. Daniel Defense’s RIS III handguard is their M-LOK answer. The barrel free-floats inside this 12.5-inch handguard that’s hard-coat anodized in Daniel Defense’s version of FDE.

DD's "bolt up" system uses six bolts to rigidly attach the RIS III handguard to the mounting plate sandwiched between receiver and barrel nut.DD's "bolt up" system uses six bolts to rigidly attach the RIS III handguard to the mounting plate sandwiched between receiver and barrel nut.
DD's "bolt up" system uses six bolts to rigidly attach the RIS III handguard to the mounting plate sandwiched between receiver and barrel nut.
Ambidextrous controls are found on the new DD4 lowers.Ambidextrous controls are found on the new DD4 lowers.
Ambidextrous controls are found on the new DD4 lowers.

Their new RIS III handguard replaces the quad rails with M-LOK attachment slots all around and a full-length 1913 rail running along the top. The handguard is held in place by six sizable bolts that attach to DD’s “bolt-up” plate, which is installed between the upper receiver and the barrel nut. The bolt-up plate has anti-rotation tabs. Perhaps the most ingenious thing about the RIS III handguard is that it uses the same bolt system as the RIS II. To change or upgrade your current Daniel Defense RIS II quad rail to the M-LOK RIS III, all you do is unscrew these six hex bolts at the rear. No gunsmithing or armorer needed. The swap involves one hex wrench and about five minutes.

Behind the handguard, you’ll see something new for Daniel Defense — bilateral (ambidextrous) controls. Daniel Defense was already offering a safety selector with levers on both sides, but now their magazine release and bolt release are as easily operated by left-handers as righties.

The ejection port cover is polymer. This is somewhat new for Daniel Defense. I was told by DD that, “The upgraded polymer ejection port cover provides a better seal, won’t rust, can’t be bent to interfere with the function of the rifle, and is about a third of the weight when compared to traditional steel ejection port covers.”

Daniel Defense’s Grip-N-Rip charging handle is ambidextrous and robustly built. Not only does it provide a larger gripping area than the GI design, but it’s also engineered to vent gas away from the shooter’s face during suppressed fire.

The bolt carrier group meets all military specifications. While this is a commercial gun, it is built to military specs: chrome-lined carrier, properly staked gas key, even a castle nut that has been staked in two places. At the back of the receiver, you’ll see the end plate has a QD sling socket. An H (heavy) buffer is installed in the gun.

The magazine well sports a slightly more aggressive bevel than found in military guns. For a pistol grip and stock, Daniel Defense uses their own designs, both with rubber overmolding. The rifle is shipped with one 32-round DD magazine. My sample was provided with a set of DD Rock & Lock fixed iron sights, but they do not come standard on the rifle.

With their short-barreled MK18, Daniel Defense supplied more upper receiver assemblies to the military then they did complete guns, and I’m sure that will be the case with this M4A1 RIII. The military, whether they should or not, has no interest in the ambi controls seen in this lower receiver.

The RIII is thinner than the quad rail previously used by SOCOM. M-LOK slots enable a multitude of accessory mounting.The RIII is thinner than the quad rail previously used by SOCOM. M-LOK slots enable a multitude of accessory mounting.
The RIII is thinner than the quad rail previously used by SOCOM. M-LOK slots enable a multitude of accessory mounting.

An honest review of this rifle wouldn’t be complete without comparing the details of the RIS III handguard to the Geissele MK16 handguard, which was chosen for the URG-I. I have no doubt the RIS III was specifically designed to meet the SOPMOD “Block III” specs. The original DD RIS II quad rail is beefy — 2.23-inches wide by 2.25-inches tall. The MK16 is the slimmest handguard made by Geissele, and it was built that way specifically at the request of the SF troopers who wanted a slim handguard. It is 1.59-inches wide by 2.22-inches tall. Daniel Defense’s new RIS III seems deliberately sized between the two: 1.95-inches wide and 2.22-inches tall according to my calipers, both a bit wider and a bit thicker than the Geissele MK16 but slimmer and smoother than the quad rail.

People call quad rail handguards “cheese graters,” as they are rough and wide. However, they have one advantage over all competing aluminum handguard designs: they take forever to heat up. You will likely be out of ammo before your quad rail handguard gets too hot to hold. Narrower handguards made of thinner aluminum get your hand closer to the heat source that is the gas block.

In addition to the requisite accuracy testing and working on my double-taps and target transitions with the M4A1 RIII, I shot it alongside a Geissele URG-I to compare heat resistance. No surprises — the Daniel Defense, with its slightly wider, thicker handguard, took longer to heat up. If you are wearing gloves or using a vertical foregrip or are a tough Special Forces operator, that’s not an issue, but for the rest of us, it is a factor. Unsurprisingly, the rifle proved reliable and soft-shooting.

Daniel Defense rifles have become the standard, go-to brand when you want a rifle that has military DNA but is equipped with upgraded features. The M4A1 RIII and the rest of the DD4 RIII family continues that tradition.


When selecting an AR carbine, we have two main choices in barrel length: 14.5 or 16 inches. Both have advantages. Before choosing, however, ask yourself one thing: Will I ever suppress this carbine? If so, it’s smart to go 16 inches. Here’s why. Daniel Defense’s M4A1 has a 14.5-inch barrel with a flash hider permanently attached — i.e., pinned and welded — to extend beyond 16 inches. This results in a compact firearm, but you won’t be unscrewing the flash hider to install a suppressor. For some shooters, that’s not an issue. For those who may want to run a can someday, consider a carbine like the DD4 RIII due to its 16- inch barrel. With flash hider installed, the overall length will be an inch and a half longer than the M4A1, but you’ll gain some velocity and retain the option to run a suppressor or muzzlebrake in the future by unscrewing the factory installed flash hider and installing a new muzzle device of your choosing.


.223 REM 5.56 NATO

Black Hills 77-gr. OTM

Federal Fusion 62-gr. SP

Wolf 55-gr. FMJ

Frontier Ammo 55-gr. FMJ

Winchester 62-gr. M855

2,600 2,752 2,878 2,905 2,818
Extreme Spread
53 55 68 77 69
Standard Deviation
30 29 28 41 40
Average Group (in.)
1.17 1.18 1.84 1.55 1.56 
Best Group (in.)
.91 .99 1.55 1.23 1.20


Accuracy results are the averages of four five-shot groups at 100 yards from a sandbag rest. Velocities are averages of 10 shots measured with an Oehler Model 35P 12 feet from the muzzle.